This exists in the three forms, soft, hard and extra hard, and the tests
made are for the purpose of ascertaining to which class the sample belongs
and hence to what uses it may well be put.
1 Determination of the Specific Gravity.—With the picnometer
in the ordinary way for solids ; very hard pitches should first be powdered.
2. Determination of the Free Carbon.—As with tar (see Crude Tar,
3, P- 3i8).
3. Determination of the Ash.—2 or 3 grams of the pitch are burnt
in a porcelain crucible in a muffle and the residue weighed.
4. Determination of the Volatile Matter and Coke.—As with fuels
(g.v.). It is important to note the appearance of the coke—whether swollen,
compact or coked.
5. Softening and Melting Temperatures.—These serve better than
other tests to indicate the degree of purity of the pitch. In a beaker of
water containing about half a litre of water is suspended a cube of the pitch
of about 13 mm. side or a disc 4-5 mm. thick at the end of an iron wire,
the pitch being 5 cm. from the bottom. A thermometer is immersed with
the bulb at the same depth as the pitch and the temperature of the water
raised 5° per minute. From time to time the pitch is withdrawn to ascertain
how it behaves when pressed between the fingers. The temperature of
incipient softening is taken as the lowest at which the pitch can be twisted
without breaking, while the temperature of softening is that at which it can
be moulded between the fingers without force and the melting point as that
at which it begins to drop.
6. Distinction between Tar Pitch, other Pitches and Natural
Asphalt.—The characters of these products are as follows:
Vegetable Pitch (Black or Marine Pitch).
Black, with an
or less stiff,
of fatty sub-
with an odour
that of vege-
Very soluble in
alcohol, giving a
part ia lly
does not give
ous matters and
for phenols ;
giving the re-
actions for phen-
ols. It colours
The distillate has
In general has
Has a saponi-
has an alka-
an acid reaction.
ber and an
21tillation use is made of a condenser, which is removed